High edge gradient silver halide emulsion



Th invention r l t s to .a photographic emulsion .of silver halide and more particularly to a photographic emulsio gi ng a age of h e adient- Th at o o c g n densi y t .dis an'cem :the boundary between the darkened part and the undarkened part of a photographic image is vcalled edge gradient. In general, the higher the ,edge gradient the sharper the image. ln-orderto obtain animage of high edge gr'adient,

a special developing solution contains a small amount of sulfite salt, having a ;high pH value and containing hydroquinone alone as developer, has been ernployed (for example, ref. Yule, J.A.C., Formaldehyde- Hydroquinone Developers and Infectious-Development, J. Frank, Inst 239,221 (1945)).

It is the object of this invention to provide a photographic emulsion Which gives an image of high contrast when a developing solution of this type isemployed.

Photosensitive materials using such emulsion are suitable for making the half-tone reproductions -by means of reproduction screens such .as glass screen and contact screen. The above-mentioned object can be attained by adding to the emulsion (1) the derivatives o'f.4- hyd-roxy- 1,3,3a-7-tetrazaindene and (2) at least one compound selected from the group consisting of lysine and arginine and their salts. The derivatives of 4-hydroxy-'1, 3,3a,7- tetrazaindene are represented by the following structural formula:

where R and R represent hydrogen atom, allsyl group, aralkyl group or aryl group, and R represents hydrogen United States Patent /CH (in Additional examples of tetrazaindenes are as follows:

0-. out

ing structural formulae:

Lysine (hydrochloride) Arginlne (hydrochloride) H:NC-NH- CH2CH2CH2$H-C O OH-H Cl 11in n11: (v1) The amount of compounds employed in this invention varies according to the sort of emulsion, but it is preferable to add 10 mgfito 1 g. of tetrazaindene, 0,1 g. to 10 g. of lysine or arginine or their salts per '1 mole of silver halide.

Photographic emulsions are prepared in the following three stages: (1) The emulsification and digestion (first ripening) of the silver halide, (2) removal of excess of salts by washing with water and the like, and (3) second digestion (after ripening) to increase the sensitivity. The compounds maybe added at any stage. Tetrazaindene may be added either before or after the addition of lysine or arginine, but it is most preferable to add these substances after the second ripening and before coating. These substances are dissolved in the solvents that have nodetrimental effect on the emulsion, for example, water, lower alcohols such as methanol and ethanol, andketones, and h a e t h cm sion- In this invention an emulsion of silver chloride, silver bromide, silver chlorobrornide, silver iodo bromide, or silver chloroiodo bromide maybe employed, but that of sil- 'e o o id smos preferable.

The emulsion maybe chemicallysensitizedby unstable compounds containing sulfur, such as ammonium thiosulfate, and allyl thiourea (ref. P. Glafkides Chimie Photographique, 2 me Edition Photochinema, Paul Montel Paris 1957, pp. 297-299), and/ or a compound of gold such as a complex of aurous compound and thiocyanic acid (ref. ibid, p. 301) according to the Well-known method in the art. The emulsion may be optically sensitized by the addition of sensitizing dyes such as cyanine dyes or merocyanine dyes (for example, ref. Shinichi Kikuchi et al. Handbook of Scientific Photograph 1959, pp.

S 1 Relative sensitivity Contrast Sharpness of dot amp e 1'30 2 15' 3' 1'30 2'15 3' rec 2'15 3' (1) 25 63 100 4 7 3 7. 0 D B C (n) 12 23 65 2. 7 5. 6 7. E C A (lll) 58 79 103 7. 7 6.9 6. 2 A C D (lv) 35 70 97 6.1 8. 1 7. 2 B A B Average slope between base density+fog density +0.1 and base density-Hog density+2.l.

-24, Maruzen Co.). The emulsion may contain a hardening agent such as chromium alum, formaldehyde, or

others (ref. ibid. pp. 29-47). In order to facilitate the 2 coating of emulsion, a surface-active agent may be added.

Tetrazaindenes have been well known as a stabilizer in the emulsion for negatives, but are employed in this invention to improve the contrast. When tetrazaindenes are used alone, the improvement of the halftone-dot due to the improvement of contrast, that is the increase of edge gradient, cannot be attained because of the decrease of developing rate. Satisfactory results can be obtained by using tetrazaindenes along with arginine or lysine.

As seen from this table, Sample iv provides sharp dots of high contrast in a wide range of time of development.

EXAMPLE 2 As in Example 1, four samples were prepared by adding 5-canboxy-4-bydroxy-1,3,3a,7-tetrazaindene (II) and/or hydrochloric salt of arginine (VI) to the emulsion. The amounts of (II) and (VI) per 1 mole of silver halide were as follows:

G./l. mole oi silver halide In order to facilitate the understanding of this inven- 30 tion, examples will be given hereafter. It should be 0 l0 realized that this invention is not limited by examples but 0.24 g 9 limited by the appended claims. M4

EXAMPLE 1 Reierence. Four samples weer prepared by adding 6-methyl-4-hy- Results of tests are summarized in the following table:

Relative sensitivity Contrast Sharpness oi dot Sample (i) 2s 63 100 4.0 7. a 7. 0 D B o n 11 20 as 2. a 4. 9 7. 5 E o A (iii) 77 90 10a 7. a 5. 7 5. 4 A o D (iv) 25 57 85 4. 2 7. 7 s. 1 B A A dnoxy-l,3,3a,7-tetrazaindene (II) and/or hydrochloride of As seen from this table, (iv) provides sharp dots of lysine (V) to the emulsion of silver chlorobromide which contains 30 mole percent of silver bromide, the optimum amounts of sensitizing dye and hardening agent, and gelatin in .a proportion of 105 g. of gelatin to 1 mole of silver halide. The amounts of (H) and (V) were as follows:

G./l. mole of silver halide Sample 1 Reference.

These samples were coated on film bases and dried. Then sensitometry and evaluation of halftone-dot were carried out using these test films.

Sensitometry Was carried out in the following manner. A test film was exposed to light, emitted from a tungsten lam-p (2666 K.) and passing through an optical stepwedge, and then developed at 20 C. in a developer of the following formula:

high contrast in a wide range of time of development.

What is claimed is:

1. A photographic emulsion of silver halide characterized in that in order to increase the edge gradient of image the said emulsion contains (1) at least one compound selected from the group consisting of 4-hydroxy-1,3,3a,7- tetrazaindenes which are represented by the following structural formula:

in which R and R represent a member selected from the group consisting of hydrogen atom and alkyl groups and R represents a member selected from the group consisting of hydrogen atom, alkyl groups, cal-boxy groups, and carboalkyl groups, and (2) at least one compound selected from the group consisting of lysine, arginine and their salts.

2. A photographic emulsion according to claim 1 wherein said compound (2) is lysine hydrochloride.

3. A photographic emulsion according to claim 1 wherein said compound (2) is arginine hydrochloride.

4. Amethod of increasing the edge gradient of image of silver halide photographic emulsion comprising adding thereto (1) at least one compound selected from the group 5 consisting of 4-hydroxy-1,3,3a,7-tetrazaindenes which are represented by the following structural formula:

lected from the group consisting of lysine, arginine and their salts.

5. A method according to claim 4 wherein said compound (2) is lysine hydrochloride.

6. A method according to claim 4 wherein said compound (2) is arginine hydrochloride.

References Cited UNITED STATES PATENTS 2,944,902 7/1960 Carroll et a1 96-107 NORMAN G. TORCHIN, Primary Examiner.

G. COHN, Assistant Examiner. 

1. PHOTOGRAPHIC EMULSION OF SILVER HALIDE CHARACTERIZED IN THAT IN ORDER TO INCREASE THE EDE GRADIENT OF IMAGE THE SAID EMULSION CONTAINS (1) AT LEAST ONE COMPOUND SELECTED FROM THE GROUP CONSISTING OF 4-HYDROXY, 1,3,3A,7TETRAZAINDENES WHICH ARE REPRESENTED BY THE FOLLOWING STRUCTURAL FORMULA: 